Web Animations: Throw exceptions for play/pause/reverse/finish with infinite end time

https://w3c.github.io/web-animations/#pause-an-animation
https://w3c.github.io/web-animations/#finish-an-animation
https://w3c.github.io/web-animations/#reverse-an-animation
https://w3c.github.io/web-animations/#play-an-animation

Added test also passes in Firefox nightly.

Review URL: https://codereview.chromium.org/1716673002

Cr-Commit-Position: refs/heads/master@{#376951}
4 files changed